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    <meta http-equiv="X-UA-Compatible" content="IE=edge">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <title>Document</title>
</head>

<body>
    <script>
        let sbo1 = Symbol()
        let sbo2 = Symbol('abc')
        let sbo3 = Symbol('abd')
        console.log(sbo1);
        console.log(sbo2);
        console.log(sbo1 == sbo2);
        console.log(typeof sbo1)
        console.log(NaN == NaN)
        console.log(undefined === undefined)
        console.log('' === '')
        console.log(null === null)

        const obj = {
            name: 'zs',
            age: 18,
            [sbo1]() { },
            [sbo2]: () => { },
        }

        /*  let eventMap = new Map();
         let on = (callback) => {
             let handler = Symbol('handler');
             eventMap.set(handler, callback);
             return handler
         };
 
         let off = (handler) => {
             eventMap.delete(handler)
         } */

        let timeid = Symbol('timeId');
        timeid = setTimeout(() => { console.log('run') }, 1000);
        // clearTimeout(timeid);

        // const COLOR_RED = Symbol();
        // const COLOR_GREEN = Symbol();

        // const COLOR_RED = "COLOR_RED";
        // const COLOR_GREEN = "COLOR_GREEN";
        // console.log(COLOR_RED, COLOR_GREEN)

        /*      export const COLOR_RED = Symbol();
             export const COLOR_GREEN1 = Symbol();
             export const COLOR_GREEN2 = Symbol();
      */
    </script>
</body>

</html>